This invention relates to the treatment of materials and, in particular, to the heat treating of materials having a carbon degradable content in order to convert the carbon degradable content to carbon.
In processes of the above type, it is often desirable that the end effect of the process is carbonization of the carbon degradable content without appreciable disturbance of certain of the other properties of the material. This is especially true in the heat treating of plates to be used to form various gas passages in fuel cells. In particular, in the heat treating of these plates, it is necessary that the surface integrity as well as the negligible through porosity of the plates be maintained. Degradation in surface integrity is evidenced by surface blistering, while increases in through porosity are evidenced by gas leakage, both of which effects could result in a decrease in performance and possible damage to the fuel cell incorporating the plates.
In one prior practice for heat treating fuel cell plates, the plates are subjected to heat which is increased at a uniform rate to the temperature at which the carbon degradable content of the plates is converted to carbon. To prevent blistering and/or an increase in through porosity beyond predetermined limits, the rate of increase in temperature is maintained quite low (i.e. at about 5.degree. C./hr.). This, in turn, requires that the processing time be quite long (i.e., about 180 hrs.). Long processing times, however, make the process inefficient and undesirable from a production cost standpoint.
It is therefore an object of the present invention to provide a heat treating practice for materials containing a carbon degradable content which does not suffer from the disadvantages of prior practices.
It is a further object of the present invention to provide a heat treating practice which is considerably more rapid than prior practices.
It is also an object of the present invention to provide a heat treating practice for fuel cell plates which can be carried out rapidly without causing surface blistering and/or appreciable increases in through porosity.